The Green party today called on the government to act to reduce the number of vehicles on the road.

"People's health has suffered directly because of the complacency and inaction of successive government ministers," Green London assembly member baroness Jenny Jones said.

"This latest admission about the extent of the air pollution problem reinforces the case against more road building in London and for the introduction of pay as you go driving to bring down fares and reduce traffic."

The government's admission comes as London's Oxford Street was named the most polluted street in the entire world, due to diesel emissions.

Levels of NO2 on the street were found to be up to ten times the safe and legal limit.

Defra today insisted pollution levels were coming down.

"We are investing heavily in measures to improve air quality and have committed billions to increase uptake of ultra-low-emission vehicles, sustainable travel and green transport initiatives," a Defra spokesperson said.

"As our understanding of NO2 evolves this must be reflected in our projections which is why we have revised these figures – work is under way to ensure compliance with EU limits in the shortest possible time."